There are more than 2 million people in US prisons. Photograph: Shannon Stapleton/Reuters

Judith Clark, a 1960s radical and the getaway driver of the 1981 robbery of a Brinks truck in Nanuet, New York, was the subject of a controversial article this Sunday, looking at her transformation in prison, and sparking a debate about rehabilitation.

At the time of the robbery, which left two police officers and a security guard dead, Judy was a member of an ultra-left group. Although she was neither a shooter nor armed – she was seated alone in one of several getaway cars – she received a sentence of 75 years to life. The sentence was so long because she refused to defend herself and made a spectacle of the courtroom.

I met Judy in 1996 at Bedford Hills correctional facility in upstate New York when, for five years, she participated in a writing group I ran. The group was mainly for long-term inmates who had committed violent crimes; the purpose was to give them a place, and a creative process, where they could come to terms with their actions, and take responsibility for their crimes, through writing – confessions, dreams, rants, memories.

It was an incredibly arduous, emotional process and in that time I got a deep look into the women in my group. I witnessed their bravery, their fear, but mainly their hunger for honesty – for themselves and each other. They were relentless in their insistence on discovering who they were, what drove them to do what they had done and, in the end, to make amends.

I know few people in the outside world who would have survived the rigour and ferocity of their self-scrutiny. It is no easy thing to say: "I have terribly hurt and sometimes even been part of destroying another person." It requires humility and breaking down your defences against an onslaught of guilt and self-hatred. It means returning to your lone cell night after night, locked away with no phone, no family and nothing between you, your aching conscience and inner demons.

Right now there are more than 2 million people in US prisons. That is approximately the population of Macedonia. The US has the largest number of prisoners per capita in the world. Yet we seldom ask why: why there are so many prisoners, what the function of prison is and whether we believe people have the potential and the right to change.

If we call these places correctional facilities, we should be serious about rehabilitation. Yet instead of offering groups, methods and programs for prisoners to address their crimes, we merely recreate violent and inhumane environments – throwing people who have often suffered violence, poverty and degradation in the earliest parts of their lives into even greater cruelty, inhumanity and violence.

Judy was sentenced to 75 years. She has already served 31. I believe she should be released now. She is a transformed person – kind, wise, moral, spiritual, devoted to others. I will stake my life that she will do good and not harm. I know there will be victims of her crimes who will be outraged by my support and sympathy for her. And I do feel their pain and suspicion; the death of police officers and a security guard, the nine children left fatherless – those lives will never come back.

But surely we can hold our anger and the memory of our murdered loved ones, and at the same time allow transformed perpetrators to offer the rest of their life to contributing to society, healing their communities, their families? This is not just a question for the victims of personal crimes and their families, but for all of us living in a world where violence is committed on a domestic, national and international scale so frequently. Instead of allowing our victimisation to frame our lives forever, we must find ways to break out of its story and boundaries.

Judith Clark exemplifies a prisoner who has undertaken the deepest psychological and spiritual journey, and faces head on where she went wrong, who she hurt and how she must change. Judy was given her sentence not because of her role in the crime, but because her attitude in court convinced the judge that she could never have the respect for human life needed to move through, and contribute to, society.

The lives lost can never be redeemed. But her attitude can and has been redeemed: she now treats human life – the lives of her fellow inmates, their families, the officers, volunteers – with incredible respect, and this respect runs through everything she does. Let's free Judy … and then I've got a long list of others.